Culture of earthworms which will be a raw material for dry earthworm powder used for health food or drugs is carried out by supplying cow manure, food waste, or the like as a feed in addition to soil in a culture bed including the soil. Generally, Escherichia coli or general bacteria are bred in the soil, and many harmful substances such as arsenic or heavy metals are contained in the soil as well as the feed supplied to earthworms. Thus, the earthworms accumulate bacteria or a harmful substance in their bodies by eating soil or feed during the growth. Therefore, it is required to remove bacteria or a harmful substance from earthworms so as to avoid adverse effects on human bodies in the production of dry earthworm powder.
In the related art, as a method for producing dry earthworm powder, from which bacteria or a harmful substance has been removed, a method in which body cavity fluids (coelomic fluid) containing casting soil and a harmful substance in the bodies of the earthworms are removed, bacteria or a harmful substance is thus removed from the earthworms, and these earthworms are used as a raw material for dry earthworm powder has been known. For example, a method in which casting soil or body cavity fluids are removed from the bodies of earthworms by a step of leaving the living organisms of the earthworms to stand in a bright place for a long period of time and a step of sprinkling powder of acids such as citric acid onto the earthworms or dipping the earthworms in aqueous solutions of the acids; the earthworms are then crushed; and the crushed products thereof are freeze-dried to produce dry earthworm powder, from which bacteria or a harmful substance has been removed, has been known (see Patent Document 1).
In addition, a method in which bacteria are further removed by subjecting the dry earthworm powder produced to heat sterilization has also been known (see Patent Document 2).